Anchored file layer adds a directory-listing size cap and new operations

What

The anchored filesystem layer is an internal part of Claude Code for working with files and folders. It gained several pieces:

• Listing a directory now has a size cap. Going over it raises the new error code WORKING_LIST_TOO_LONG, with the message "the directory holds more names than may be listed".
• The WORKING_LIST_UNSUPPORTED message grew from "this backend cannot list a held directory" to "this backend cannot list a held directory, or cannot stop at the bound that was set".
• createAndOpen and anchorBeneath (a nested anchor) are new operations.
• removeTree now accepts a keep entry and an onDeleted callback, which is code run as each item is deleted.
• A path prefix is now passed through when creating and opening files.

Why

These are internal changes with little direct effect on how you use Claude Code. The most visible one is that a directory with too many entries can now produce the "more names than may be listed" error instead of being listed in full.